It's a process.
1. He should have to play with younger kids and "let" them win. So he get the concept. 7 may be young for this but he should be able to do this pretty well by 10.
2. He should also play with older friends/cousins etc because he will hold his emotions better for them - but also you may want to say to the older kid that he is not good at losing and you are working on it so they are prepared.
3. I had a rule at 7 - you can cry but you have to wait until you get to the car. For the house - if you are going to lose it - go to your room first.
4. My kids tend to say "he cheated" when they lose or say "the referee was terrible". While this is a hard one I am very strict about not blaming the referee. I say there is no such thing as a perfect game refs miss calls period - it is part of the game. As you get older - there is cheating, etc. I say you can't lower yourself to their level.
5. Not wanting to lose and getting emotional is normal for some/most and it is good to be competitive but not good to be a butt head. So I always say "you know that feeling you have in your chest, it's a normal feeling, now what you do with that feeling is the only thing you can control." This is not possible at 7 but very possible at 13 so they need to learn this and it is a process.
I have a rule that my son and H can't talk about a game for a minimum of 30 minutes after the game is over if it is a hard lose - like the championship or something like that. Even at 7 a championship is a big deal.
I also have 1 that I wish cared just a little.